The present invention relates to a structure of a power train system comprising an engine, an electric rotary machine (hereinafter, one primarily used for driving is called as an electric motor, one primarily used for generating power and starting an engine is called as a power generator and one used for driving and generating power with generally the same frequency to each other is called as a motor generator) and a gear change mechanism, and more particularly to a power transmission apparatus for improving a transmission efficiency of a power train system.
In view of a problem of global environment, it becomes important to establish a hybrid control system for motor vehicles, in which a great reduction of specific fuel consumption can be expected.
In JP-A-10-217779, there is disclosed an integrated hybrid power transmission apparatus constituted by a single electric rotary machine, a speed change gear mechanism and a clutch mechanism. The apparatus disclosed in the publication is so constituted that the gear change mechanism having the electric rotary machine and the clutch mechanism is integrally contained in a housing of the power transmission apparatus to make the power train system compact and light in weight. Further, by always connecting an input shaft of the gear change mechanism with the electric rotary machine, it is possible to take a driving manner so-called xe2x80x9ca series hybrid systemxe2x80x9d in which an engine drives only the electric rotary machine to generate a power by a part of which other electric rotary machines are driven to run a vehicle. The engine and the electric rotary machine are totally controlled so as to satisfy a feeling of speed acceleration and deceleration desired by a driver and operate the engine and the electric rotary machine in a high efficiency zone.
The system shown in JP-A-10-217779 has the following problems.
First, in order to reduce a torque shock during changing a gear change ratio, for example, from a first speed to a second speed or from a second speed to a third speed, it is necessary to arrange the electric rotary machine in a drive wheel side to the gear change mechanism. On the contrary, in order to generate power by the engine drive force in the series hybrid manner, it is necessary to arrange the electric rotary machine In the engine side to the gear change mechanism. Accordingly, in order to prevent the gear change shock and also improve the gear change performance, at least two or more electric rotary machines are required, resulting in a problem that the drive system becomes a large size.
Second, since a torque transfer mechanism of the engine output shaft to an electric rotary machine output shaft is complex, an efficiency of torque transmission is low.
Third, since the drive system is so constituted that the electric rotary machine is driven by the engine, an inertia torque of the rotor of the electric rotary machine is exerted on the engine side as a load. Thus, during running under the engine drive, in order to correctly execute an acceleration command from the driver, it is necessary to generate an additional torque for canceling the inertia torque in the engine side as well as the torque corresponding to the acceleration command. This poses a problem that the specific fuel consumption is deteriorated in order to improve a driving performance.
Accordingly, an object of the present invention is to improve a transmission efficiency, reduce a specific fuel consumption of a vehicle and make a drive system compact, in a power transmission apparatus constituted by a gear change mechanism having an electric rotary machine and a clutch mechanism.
Under the object, there is provided an improved mechanism of a gear change apparatus according to the invention.
With respect to the first problem, it is effective to dispose a mechanism of mechanically reducing a gear change shock in place of employing an electric drive force such as an electric rotary machine for reducing the gear change shock. Accordingly, the invention is of a power transmission apparatus of motor vehicles, which has an engine, a gear change apparatus arranged between the engine and a vehicle drive shaft, an electric rotary machine connected to an output shaft of the engine and the vehicle drive shaft via the gear change apparatus, and a clutch arranged between an input shaft and an output shaft of the gear change apparatus and regulating a transmission torque between the input and output shafts. According to the clutch, it is possible to reduce the gear change shock generated during the gear change operation without arranging the electric rotary machine in the drive wheel side of the gear change apparatus.
Preferably, the power transmission apparatus of motor vehicles comprises the clutch mounted on a gear of a minimum gear change ratio in the gear change apparatus. By mounting the clutch on the gear of the minimum gear change ratio (i.e. the high speed side gear), it is possible to meet any change of rotation speed before and after the gear change operation.
Further, more preferably, the power transmission apparatus of motor vehicles is structured such that the clutch is provided in a gear having a speed change ratio equal to or more than 1 in the gear change apparatus. By providing the clutch in the gear having the speed change ratio equal to or more than 1, for example, the third speed change ratio in the gear change apparatus having the speed change ratios from the first speed change ratio to the fifth speed change ratio, it is possible to start by the clutch in the case that the clutch for starting is in trouble.
With respect to the second problem, the following technique will be possible. That is, in the hybrid vehicle, in order to improve the specific fuel consumption of the engine, there may be a case of stopping the engine when stopping the vehicle and using the electric rotary machine for starting the engine at every time of starting the vehicle. In this case, in view of an electric efficiency, it is effective to reduce and transmit the rotation of the electric rotary machine to the engine shaft via the gear change apparatus in place of directly transmitting the rotation to the engine shaft. Thus, according the invention, there is provided a power transmission apparatus of motor vehicles having an engine, a gear change apparatus arranged between the engine and a vehicle drive shaft, and an electric rotary machine connected to an output shaft of the engine and the vehicle drive shaft via the gear change apparatus, wherein a rotation of an output shaft of the electric rotary machine is reduced and transmitted to an engine side input shaft of the gear change apparatus.
Further, in the case of driving the electric rotary machine by an engine power to generate electric power, it is effective to restrict the number of transmission mechanisms for transmitting the engine power to the electric rotary machine (e.g. the number of gears) to be small. Thus, according to the invention, there is provided a power transmission apparatus of motor vehicles having an engine, a gear change apparatus arranged between the engine and a vehicle drive shaft, and an electric rotary machine connected to an output shaft of the engine and the vehicle drive shaft via the gear change apparatus, wherein the output shafts of the engine and the electric rotary machine are provided separately, and gears respectively mounted on the both shafts for transmitting the power of the both shafts directly engage with one another. By the direct engagement of the gears without interposing another gear therebetween, it is possible to restrain a reduction of the efficiency of power transmission.
More preferably, the present invention relates a power transmission apparatus of motor vehicles further having a clutch for breaking the connection between the output shaft of the electric rotary machine and the input shaft of the gear change apparatus at the electric rotary machine side. According to the clutch, it is possible to optionally break the connection of the engine and the electric rotary machine and prevent the inertia torque of the electric rotary machine from being exerted on the engine side as a load, thereby the third problem mentioned above can be solved.
A description will be in detail given below of an embodiment according to the invention referring to the accompanying drawings.